Aiming at the problem of large deformation of arch shoulder in deep high stress roadway of Hudi Coal Mine, through field sampling, experimental test and numerical simulation, the deformation mechanism of arch shoulder under the coupling action of high stress, soft and hard rock strata of roof, weakening of surrounding rock and disturbance of space staggered roadway was revealed. Through the research results, the high stress increases the range of the plastic zone, and the soft and hard rock strata lead to the change of the expansion form of the plastic zone. With the decrease of the vertical distance of the space staggered roadway, the insufficient bearing capacity of the supporting material and other factors lead to the increase of the deformation of the shoulder angle and the side, forming the deformation characteristics of the arch shoulder. Based on this, the active and passive collaborative control technology is proposed, and the targeted support concept of “unloading control + strong support + collaborative” is adopted. The optimization scheme controls the deformation of roadway within 8

Roadway intersection point are critical in underground mining and significantly impact mine safety.To address challenges such as large unsupported roof areas,concentrated stress,and difficult support in deep complex intersection point,a study is conducted at the-650 south wing track main roadway intersection point in Yangcheng coal mine.The re-search combines theoretical analysis,numerical simulation,indoor testing,and field application to evaluate intersection point stability and develop composite support technologies.By analyzing geological and mechanical parameters,a vari-able cross-section beam support model is established,and a formula for roof deflection is derived.The roof span is identi-fied as the primary factor affecting intersection point stability,with a defined danger zone for roof subsidence.Two com-posite support schemes are designed:One using concrete-filled steel tube composite frame and another using concrete-filled steel tube pier column group.Simulations show roof subsidence of 100 mm and 150 mm,respectively,indicating both schemes effectively controlled subsidence and ensured safety.A comparative analysis base on construction difficulty,cost,and allowable deformation selected the concrete-filled steel tube pier column group scheme as optimal.Field imple-mentation confirms significant improvements in roof and surrounding rock stability.Monitoring data after 2 years and 5 years show cumulative roof subsidence of 65 mm and 126 mm,respectively,lower than predictions for the concrete-filled steel tube support scheme.This demonstrates continuous stability,good support performance,simple construction,and economic feasibility,providing valuable insights for complex intersection point support.

Current ASCE 7 seismic provisions often neglect the interaction between steel and reinforced concrete (RC) parts in steel-reinforced concrete vertical hybrid structures, which may lead to unconservative seismic demand estimates. To address this issue, two two-storey steel-reinforced concrete hybrid frames with wing walls were tested under cyclic lateral loading. Two transfer connection systems were examined: a partially embedded transfer connection (PETC) and a conventional embedded connection (EC). Test results showed that plastic hinges did not form at the bases of steel columns, while damage initiated in RC beams and wing walls prior to RC column yielding. Compared with the EC specimen, the PETC specimen exhibited improved load-carrying capacity, enhanced energy dissipation, and a more desirable flexural failure mode instead of shear failure. These findings highlight the critical role of steel-RC interaction and transfer connection details in governing seismic behavior. A plastic model was further developed to predict the load-carrying capacity of hybrid frames, showing good agreement with test results (with a mean predicted-to-tested ratio of 1.03 and a coefficient of variation of 0.07). The findings provide experimental evidence and simplified calculation method that support the seismic design and practical application of multi-storey steel-reinforced concrete vertical hybrid structures.

This paper presents experimental and numerical investigations on the flexural behavior of carbon fiber-reinforced polymer (CFRP)-strengthened circular concrete-filled steel tubes (CFST) beams incorporating internal steel stiffeners. Twelve CFST specimens were tested under pure bending to analyze their failure modes, moment-deflection relationships, stiffness, curvature deformation, and strain distributions. A finite element (FE) model was developed and validated to assess the failure mechanism, interaction among components, and the neutral axis distribution pattern. Key influencing parameters, including the material strength, nominal steel ratio of steel tube and encased lattice angles, and CFRP thickness, were systematically examined. The results demonstrate that, compared with conventional CFST members, the flexural capacity of CFRP-strengthened circular CFST beams incorporating internal steel stiffeners is positively influenced by the number of CFRP layers and their tensile strength, while the encased lattice angles further enhance structural performance. Additionally, based on superposition theory, design methods for predicting the flexural bearing capacity of such members were proposed, incorporating the contributions of CFRP and lattice angles. Accuracy analysis confirms that the proposed method provides reliable and conservative predictions.

Concrete-filled steel tube (CFST) columns reinforced with latticed steel angles (LSA), referred to as CFST-LSA columns, have been widely adopted in practical engineering. Understanding their mechanical behavior under eccentric loading is crucial for ensuring structural safety and performance in engineering applications. Previous experimental studies have demonstrated that the incorporation of steel angles substantially improves both the axial capacity and ductility of CFST-LSA columns. Existing methods for determining the eccentric bearing capacity of CFST-LSA columns primarily rely on the normalized N/Nu-M/Mu interaction curve. However, this approach involves a complex calculation procedure for evaluating the eccentric bearing capacity. To address this limitation, this study proposes a theoretical model based on the limit equilibrium method to predict the eccentric bearing capacity of CFST-LSA columns. The proposed model explicitly integrates fundamental geometric and material parameters, thereby enabling a more efficient and programmable calculation of the eccentric bearing capacity. Comparisons between the proposed model and experimental results show good agreement, with a tested-to-predicted eccentric resistance ratio of 1.085 and a coefficient of variation (COV) of 0.022. The proposed model can serve as a practical calculation method for eccentric loading of CFST-LSA columns, facilitating their application in high-rise buildings and long-span bridges.

Deep rock masses are increasingly at risk of destabilization and disaster due to “strong disturbances” and “high geostress”. Conducting rheological disturbance effect theoretical research is a key part of controlling the stability of deep rock masses. Among these, the identification and analysis of the sensitive neighboring areas affected by rock rheological disturbance effects is an important component. This study, under different confining pressure conditions, subdivides the axial stress levels of red sandstone rheology, selecting stages of cumulative residual deformation development under rock rheological disturbance effects (attenuation stage, near constant speed stage, and acceleration stage). It combines the consistency correlation between the rheological disturbance effects and the dynamic response of the micro-pore structure of the rocks, analyzing from multiple perspectives the evolutionary characteristics of the sensitive neighboring areas affected by red sandstone rheological disturbance. The results show: ① Under different confining pressure conditions, the development stages of cumulative residual deformation in red sandstone rheological disturbance show characteristics similar to static rheology. With the increase of confining pressure, the response characteristics and rates of different stages change significantly, thereby affecting the stability and strength of the rock mass. ② Using the rheological disturbance sensitivity correlation coefficient of the rocks, the sensitive neighboring areas of red sandstone rheological disturbance are further divided into weakly sensitive and strongly sensitive areas, and it is pointed out that the weakly sensitive area should be considered a key stage in the stability protection of rheological rock masses. ③ By integrating the response analysis of macro and micro damage evolution characteristics under different confining pressure conditions, an increase in confining pressure leads to a contraction of the range of red sandstone rheological disturbance sensitive neighboring areas and a reduction in the weakly sensitive intervals, accelerating the transformation towards strongly sensitive characteristics. At the same time, with the increase of confining pressure, the failure development rate of red sandstone in the strong sensitive neighborhood also increases. This study, through a comprehensive analysis of the dynamic response of the micro-pore structure and macroscopic deformation of red sandstone under rheological disturbance effects, reveals from multiple perspectives the dynamic evolutionary characteristics of the sensitive neighboring areas affected by red sandstone rheological disturbance effects, providing a theoretical basis for the safe mining and stability assessment of deep rock masses.

To investigate the load-bearing and yielding performance of grout-lifted compressible concrete-filled steel tube composite columns (referred to as "compressible columns") and to verify their compliance with the "preset and restricted deformation" requirements for roof control in gob-side entry, axial load-bearing tests were conducted on six concrete-filled steel tube composite columns. By comparing the load-displacement curves, load-strain curves, and failure modes of each column, the differences in load-bearing performance between the compressible and noncompressible columns were analyzed. This study explored the effects of slenderness ratio, outer diameter, and yielding capacity on the axial load-bearing performance of columns. The tests demonstrated that the compressible columns exhibited considerable yielding effectiveness, with the yielding structure mitigating the progression of buckling deformation. The ultimate yielding amount of the compressible columns ranged from 175 to 227 mm, with a compressibility rate of 62-87 % of the yielding structure's initial height (260 mm), equivalent to approximately 10 % of the total column length. After compaction, the internal yielding structure continued to act in tandem with the lower concrete-filled steel tube under compressive loads. The compressible columns exhibited ultimate load-bearing capacities in the range of 2859-4500 kN, which were 13-24 % higher than those of noncompressible columns of similar dimensions, indicating strong load-bearing characteristics. The failure modes were primarily bulging-and bending-deformation-induced instabilities. Based on the ultimate state of the compressible columns, which was the failure control of concrete-filled steel tubes in the lower section, and by adopting the thin-walled cylinder theory and the Von Mises yield criterion, the ultimate bearing capacity calculation formula for compressible columns was also derived:N0 = phi e phi l (beta fsAs + gamma fcAc), R2 was close to 1, the calculated values of the formula were in good agreement with the test results. This formula guided the design of the gob-side entry support design at Yangcheng and Luxi coal mines, utilizing columns with Phi 245 x 10 and Phi 299 x 10 specifications, respectively. Self-adaptive spherical bearings were incorporated to prevent eccentric loading and optimize the support design. The implementation effect of the compressible columns support was well, with economic efficiency and construction convenience, providing a theoretical basis for the application of roadside support in deep mines with high ground stress, such as gob-side entry and roadway excavation.

The wind field environment surrounding long-span bridges is characterized by its complexity and variability, resulting in wind speed exhibiting random, nonlinear, and uncertain behavior. To enhance bridge safety and mitigate the impact of wind speed, it is crucial to establish a reliable wind speed prediction model. In this study, a structural health monitoring (SHM) system was deployed on a long-span bridge to collect extensive wind speed data, which was subsequently denoised using the wavelet decomposition (WD) method. Leveraging the long short-term memory (LSTM) approach, a wind speed prediction model (WD-LSTM) was developed. The study focuses on investigating the effects of three different thresholds (Bayesian threshold, SURE threshold, and Minmax threshold) in the WD method, the number of hidden units (2, 4, 8, 16, 32, 64, 128, 256, and 512) in the WD-LSTM model, and the number of inputs (one-step prediction, five-step prediction, ten-step prediction, and twenty-step prediction) in the WD-LSTM model on the prediction performance of wind speed. Evaluation metrics such as RMSE and R2 are employed for this analysis. Furthermore, the calculation time of the WD-LSTM prediction models with different hidden units and inputs is compared. Finally, an optimal WD-LSTM prediction model is proposed, taking into account both prediction accuracy and calculation time.

The circular concrete-filled double steel tubular (CFDST) column with hoops is a promising type of composite column, characterized by annular ribbed reinforcement bars welded onto the exterior surface of the steel tube. The confinement effect is expected to be enhanced by the inclusion of hoops, allowing for the use of thinner steel tubes and reducing overall steel consumption. In this paper, the compressive behavior of CFDST columns were experimentally and analytically investigated. The objectives are to gain insights into the different performance of CFDST columns from their counterparts without hoops and to evaluate different confinement models among double-tube, double-tube with hoops, and single-tube confined concrete. The test results indicated that hoops can improve the ultimate strength by 2 %-25 % for the CFDST columns, while the ductility of the CFDST columns can be significantly enhanced. Compared to increasing the cross-sectional area of steel tubes, incorporating hoops offers greater economic benefits for enhancing the strength of CFDST columns. The composite effect can be improved by the combined confinement provided by the double steel tubes and hoops. Comparisons of the test results with existing structural design provisions highlighted the necessity to account for the combined confinement effect of the double steel tubes and hoops on the structural response of CFDST columns. Accordingly, new confinement models were proposed to predict the ultimate strength of CFDST columns without and with hoops under axial compression.

Although concrete-filled double-skin stiffened steel tubular (CFDSST) members have been researched and applied in recent years, their use in truss T-joints has been lacking. This paper therefore examines the mechanical behaviour of CFDSST chord-to-hollow steel section (SHS) brace T-joints under axial brace loading. Detailed finite element models for CFDSST-to-SHS T-joints are firstly validated by assessing the modelling approaches against recent tests for CFDSST columns and other types of T-joints. The models are subsequently used to conduct parametric assessments into the influence of key factors, including the brace-to-chord width ratio, brace-to-chord thickness ratio, material strengths, hollow ratio of CFDSST chord, and the axial load applied on the chord. It is shown that the ultimate load capacity of the T-joints increases with the increase in the brace-to-chord width ratio as well as with higher steel tube and sandwiched concrete material strength, with a much less pronounced influence from the brace-to-chord thickness ratio. A new parameter representing the flexural stiffness-to-member length ratio of the chord to the brace is also introduced, based on which the failure modes are separated into two categories related to either the failure of the brace or of the chord. Using the detailed results and observations, existing methods for determining the bearing capacities of T-joints are evaluated, leading to the development of a new design approach. The proposed design procedure is shown to provide accurate predictions for CFDSST-to-SHS T-joints, indicating its suitability for use in practical application.

The mudstone-clay composite roof roadway exhibits distinct transversely isotropic characteristics, rendering the prediction of uncoordinated deformation in surrounding rock complex and challenging. Based on transversely isotropic theory, the deformation parameters of mudstone-clay composite in different directions are calculated by true triaxial experiment, and the elastic modulus is determined as the key parameter affecting the uncoordinated deformation of composite roof roadway. The stress and strain expression of roadway surrounding rock is theoretically deduced, and the utilization of ultra-high strength bolts is proposed to control the uncoordinated roadway deformation. The results indicate significant variations in the elastic modulus of the mudstone-clay assemblage in both horizontal and vertical directions, with Poisson’s ratio showing a narrow range of variation. The composite with saturated clay exhibits reduced deformation resistance and more pronounced transverse isotropy compared to the composite with dry clay. The stress concentration is highest near the inflection point of the roadway. The roadway ribs experience vertical stress increase and horizontal stress decrease, while the roof and floor strata mainly undergo vertical stress decrease and horizontal stress increase. The strain in roadway surrounding rock mainly shows vertical strain, especially with the roadway roof exhibiting the highest vertical strain peak and the largest influence range. The vertical strain of roadway surrounding rock can be significantly reduced by increasing the value of its vertical elastic modulus E2, if it is less than 0.15GPa. However, value higher than this has little effect on the strain. According to the field observation, the utilization of ultra-high strength bolt support (E2 > 0.15GPa) in comparison to Q235 threaded steel resin bolt support (E2 < 0.15GPa) demonstrates a significant reduction in roadway uncoordinated deformation, thereby validating the accuracy of theoretical research.

This paper investigates the mechanical response of axially loaded FRP-confined square CFST columns strengthened with internal latticed angles (F-SRCFST) through experimental and analytical methods. The influence of three parameters on the performance is examined, including dimensions of the specimens, configuration of latticed steel angles, and number of CFRP layers. Experimental results demonstrate that concrete crushing in the specimens confined by CFRP exhibits a higher degree of uniformity, with cracks appearing more densely. The latticed steel angles can prevent the development of concrete cracks into the core concrete, while noticeable local buckling of the steel angle between the battens is observed. The enhancement coefficient of steel angles on the load-bearing capacity and energy dissipation ability of F-SRCFST columns is more pronounced when compared to CFRP. The utilization of CFRP and latticed steel angles can effectively improve the problem of inconsistency in square steel tube deformation under axial loading, and both parts exhibit similar effects on the dilation behavior of square CFST columns. A composite confined model was developed to consider the triple constraints of CFRP, external steel tube, and latticed steel angles, and a predictive formula was developed to estimate the load-carrying capability of F-SRCFST columns. The comparative study shows that the predictive formula agrees well with the ultimate axial strengths of F-SRCFST columns.

This study investigates the axial compression behaviour of steel-reinforced concrete-filled steel tube (SRCFST) columns reinforced by combined steel ring and carbon fibre-reinforced polymer (CFRP). A total of 24 designed columns underwent axial compression tests, featuring variations in steel tube dimensions, lattice angles, steel ring configurations, and CFRP utilisation. The underlying mechanisms behind the effects of multiple experimental parameters on the columns' axial behaviour have been delved into. The results consistently indicate that the predominant failure mode in all specimens was the steel tube's localised buckling. However, introducing steel rings and CFRP effectively reduced this buckling occurrence. Determining optimal spacing of steel rings emerged as crucial considerations for enhancing the load-carrying capacity of the specimens. The synergistic reinforcement of steel rings and CFRP not only resulted in a notable increase in the ultimate strength but also improved the ductility of the SRCFST specimens. Lastly, a design formula was developed to predict SRCFST column strength reinforced with both steel rings and CFRP. The formula's validity was verified through a comprehensive comparison between experimental and calculated values, affirming its reliability in safely predicting the ultimate strength of structural components.

The eccentric compression behavior of the CFSTs reinforced with inner latticed steel angles was experimentally investigated, and test results, such as the load–displacement curves, load‐strain curves, distributions of lateral deflection, and ultimate load, were obtained and analyzed. Test results showed the influence of the latticed steel angles on the ultimate load was not obvious when the steel consumption was relatively small, and the lateral deformation was not obvious when the compression load was smaller than 80% of the ultimate load. The corresponding finite element (FE) model was established and validated by the test results, and parametric analysis was also conducted subsequent to validation. The analysis results showed the contribution of latticed steel angles to the ultimate load would be diminished as the eccentric distance increases. Moreover, the design equations for the ultimate load were proposed based on the FE results, and the calculation results indicated the proposed design equations can predict the ultimate load conservatively and safely.

The bending mechanical properties of FRP-confined square concrete-filled steel tubes (CFST) reinforced with internal latticed steel angles, including the failure modes, characteristic curves and characteristic mechanical parameters of tested specimens, were investigated through experiments in this paper. The bending mechanisms were also analyzed using an established finite element model, including the analysis of the bending moment borne by each component, the distributions of contact pressure between different components at the mid-span section, and the distributions of the neutral axis under the bending capacity. The key influential parameters, including the tensile strength and thickness of the FRP, were also examined. The results indicate that the FRP has almost no influence on bending stiffness, however, it enhances the yield bending moment and bending capacity to a certain extent. It was also found that the enhancement decreases as the width of steel tube increases, and the influence of FRP is more profound before reaching the peak load. The calculation formulas for the bending capacity were developed using the superposition method and numerical fitting method. Analysis of their accuracy shows that the formulation using the superposition method yields relatively accurate and safe prediction results, with the prediction errors of less than 20 %.

High in-situ stress and mining disturbance will lead to the deformation and instability of deep rock mass. Under the action of high in-situ stress, deep rock mass enters the strength limit neighborhood, and the rock mass entering the strength limit neighborhood is very sensitive to mining disturbance. Research on micro-damage test of rock rheological disturbance effect is the key to solve the problem. In order to meet the test requirements in the research process, a micro-damage test system for rock rheological disturbance effect was developed. The test system optimized the host of the tester by upgrading the disturbance loading device, and expanded the micro-damage test function of rock rheological disturbance effect. The test results show that: ① The performance of rock rheological disturbance effect micro-damage test system is reliable, which is suitable for the related research of rock rheological disturbance effect micro-damage test; ② When the rock enters the strength limit neighborhood, the growth rate of large-sized pores with a pore size greater than 1 μm is much larger than the growth rate and pore compaction amplitude of small-sized pores with a pore size less than 1 μm, resulting in irreversible damage inside the rock; ③ Under different confining pressure rheological disturbance conditions, when the specimen is outside the strength limit neighborhood, the confining pressure has a certain inhibitory effect on the expansion and development of the pores of the specimen, and the compaction amplitude of the pores inside the specimen is greater than its expansion amplitude. With the increase of confining pressure, when entering the strength limit neighborhood, the existence of confining pressure accelerates the expansion and development of pores to a certain extent, and the internal pores of the specimen are dominated by expansion and development; ④ The microscopic criterion for the rock to enter the strength limit neighborhood is determined, that is, when the proportion of large-sized pores with pore size greater than 1μm increases significantly under the condition of rheological disturbance, it indicates that the rock has entered the strength limit neighborhood.

To study the mechanical properties and failure mechanism of short concrete columns reinforced with carbon fiber reinforced polymer (CFRP) strips and concrete canvas (CC), 38 short concrete columns with variable CFRP strip width, number of CFRP layers, and section form and with and without reinforcement bars were subjected to axial compression, and the damage of the strengthened specimens was monitored with acoustic emission (AE) technology. The test results show that the strength and ductility of the reinforced specimens are increased by 59-96 % and 108-126 %, respectively over those of the unreinforced ones. Reinforcement bars and concrete strength grade have little impact on the bearing capacity of the jointly reinforced specimens. The constraint effect of CC increases with increasing CFRP strip width. The columns form strong and weak constraint areas that correlates with the areas wrapped with strips and not wrapped with strips. With increasing strip width, the energy released when the specimen fails increases, and the ductility increases. These data are used to establish a strength calculation model for a short concrete column constrained with CFRP strips and CC. This model shows high fitting accuracy with the test results and can be used as a reference for practical reinforcement projects.

The bending properties of square CFSTs (concrete-filled steel tubes) reinforced with internal latticed steel angles were experimentally investigated through four-point bending test, and test results of moment vs deflection curves, moment vs strain curves, bending capacity and concrete cracks were acquired, the test results showed that the latticed steel angles can restrain the cracking of concrete and delay the upwards movement of the neutral axis. After the experiment, firstly, the corresponding finite element (FE) models were established by ABAQUS and validated through comparison with test results; secondly, the bending mechanisms of the tested specimens were analysed and discussed; thirdly, the parametric analysis was conducted to investigate the influence of the main parameters, such as the yield strength and thickness of steel tube, the yield strength and area of latticed steel angles. The research results indicated that the steel tube contributed the most to the bending capacity, hence the yield strength and thickness of steel tube have the most significant influence on the bending capacity. Moreover, the design equations for the bending capacity were proposed based on the superposition method and plastic stress distribution method, and the calculation results showed that the design equations can conservatively and safely predict the bending capacity.